It is known to take up fibrous material successively from bales of fibers of varying origins (U.S. Pat. No. 3,443,285) in quantities according to a previously determined mixture ratio by means of pincer-like grippers whereby fiber bales of the same type of fiber are suitably placed in fiber collection points (U.S. Pat. No. 3,577,599). This has the result that small amounts of fibers are mixed in a predetermined ratio during the taking up process. However, this may have the result that the mixture ratio of one type of fiber is very small, whereas the proportion of the other type or types of fiber(s) may be relatively large. In order to keep as near as possible to the small quantity of the mixture ratio, it is essential to keep the fiber quantity picked up by the gripper as small as possible. The pincer-like gripper is, therefore, set to a correspondingly small opening width. This, however, leads to a drop in productivity in the take-up device since only a small quantity of fibrous material is also picked up from the bales of the fiber collection points containing the types of fibers with the relatively large mixture ratio. Therefore, the grippers have to be brought into engagement with the bales more frequently until the correct proportion of the particular predetermined ratio has been achieved.